Well bit



Nov. 7, 1 939.

T. A. CREIGHroN ErvAL WELL BIT Filed June 17, 1938'. 2 sheets-sheet 1Nov. 7, 1'939. `T. A. cRElGHToN r AL v 2 Sheets-Sheet 2 Filed June 17,1958 M l www @HN y@ www@ ww w Ivn I| IIN Patented Nov. A7, 1939 UNITED.STATES PATENT oFFlcF.`

Thomas A. .Creighton ma Thomas E. Meantime4 Long- Beach, Calif.,assignors oi' one-third to Martha H. Wright, Los Angeles. Calif.

Application June 17, 1938, Serial No. 214,234

9 Claims. (Cl. 2551-72) the bit free and clear for the reception of thesur- This invention relates to well drilling toolsand relates moreparticularly to well bits for use in the rotary method ofwell drilling.A general object of this invention is to provide a simple, practical andeffective well bit that facilitates the surveying of the well as thedrilling progresses.

` Rotary well drilling bits have been vintroduced having openings forreceiving surveying instruments, and the like, to permit the making ofwell l0 surveys and well tests without the necessity of withdrawing thebits and drilling strings from the wells. A bit of the class justmentioned usually has a central vertical opening of substantial diameterfor passing the surveying instrument. It is necessary to arrange aremovable core receiving barrelror a removable core destroying device inthis opening to receive or cut away the core as the drilling progressesso thai-l the surveying instrument may be entered through the opening inthe bit. In employing a bit of the class referred to it is necessary toremove the core barrel or the core destroying device from the bit when asurvey is to be made. 'Following the surveying operation it is necessaryto lower or run the core barrel or core destroying device down throughthe drilling string to its position in the bit. These operations aretime` consuming and, therefore, expensive.

Another object of this inventionis to provid a rotary well drilling bithaving an opening through which a surveying instrument may be passed tomake a survey and embodying means for breaking or cutting away the coreof earth formation, that would. otherwise occupy said opening, that isretractable to permit the successful operation of the surveyinginstrument.

Another object of this invention is to provide a rotary well drillingbit of the character mentioned in which the core cutting or corebreaking means does not have to be removed from the bit to make a surveyby an instrument passed down through the bit.

Another object of the invention is to provide a bit of the charactermentioned in which the core breaking means automatically returns to theopveying instrument. v

Another object of this inventlonis to provide a well drilling bit of thecharacter mentioned in which the core breaking means is simple tomanufacture and inexpensively embodied in the bit.

A further object of this invention is to provide a rotary well drillingbit of the class mentioned in which the core breaking means cannot foulor injure the well surveying instrument.

The various objects and features of my invention willbe fully understoodfrom the following detaileddescription of typical preferred forms andapplications of the invention, throughout which description reference ismade to the accompanying drawings, in which:

Fig. 1 is a side elevation of a rotary well drilling bit embodying oneform of core breaking means.

Fig. 2 is an enlarged bottom elevation of the lower part of the bitshown in Fig. 1. Fig. 3 is an enlarged fragmentary vertical detailedsectional view taken' as indicated by line 3--3 on Fig. 1.

Fig. 4 is a horizontal detailed sectional view taken as indicated byline 4 4 on Fig. 3. Fig. 5 is a fragmentary vertical detailed sectionalview'I of the lower portion of the bit shown in Fig. 1 illustrating apart of a surveying instrument in broken lines and showing the dog inthe retracted position. Fig. 6 is a side elevation of a rotary welldrilling bit embodying another form of core breaking means of theinvention. Fig. 'l is a vertical detailed sectional view taken asindicated by line 1 1 on Fig. 6 with broken lines illustrating theretracted positions of the dogs. Fig. 8-is a horizontal detailedsectional view taken as in,- dicated by line 8-8 on Fig. 7, and Fig. 9is a fragmentary vertical sectional view of still another form of theinvention.

The present invention may be embodied in rotary well drilling bits ofvarious types and constructioris. In the following detailed descriptionwe will describe two typical forms of the invention embodied in dragtype rotary bits. It is lto be understood that the invention is not tobe construed as limited or restricted to these specic forms orapplications of the invention. Further it is to be understood thatxwhere reference isv made herein to surveying instruments and surveyingoperations it is contemplated that such referf ence is to be construedas meaning various instruments and operations that may be employed fordetermining, testing and receiving the various conditions in the well,such as directional conditions, temperature conditions, pressureconditions, formation conditions, etc.

The bit construction of the present invention illustrated in Figs. 1 to5, inclusive, of the drawings may be said to comprise, generally, a bitbody I0 having a central vertical opening II for receiving a surveyinginstrument A, cutting means I2 on the body I0 for cutting the well boreto gauge and means I3 for cutting or breaking away the core or centralportion of the earth formation.

The body I0 of the bit illustrated in Figs. 1 to 5, inclusive, of thedrawings is in the nature of an elongate Istem or shank. The lower majorportion of the bit body I 0 is cylindrical and of uniform diameter whilethe upper portion I4 of the body is enlarged and tapered downwardly andinwardly. Means is provided at the upper end of the body Inforfacilitating its connection with a well drilling string. In the typicalcase illustrated a tapered screw threaded socket I5 is provided in theupper portion of the body I0 to receive a correspondingly shaped pin onthe lower end of the string. The opening II extends downwardly throughthe body I0 from the socket I5 to the lower end of the body. The openingII serves to handle or conduct the circulation uid and is proportionedto receive or pass the surveystrument A. Means are provided in the bodyV||l to assist in locating and supporting the surveying instrument A. Anannular flange I6 is provided on the wall of th opening II. The ange I6is spaced below the socket I5. The lower portion of the opening II isreduced in diameter to receive the instrument A with suitable clearance.The flange I6 and the reduced lower portion of the opening II serve tocenter and locate the surveying instrument A in the body I0 of the bit.i

The cutting means I2 is provided to cut away the earth formation andform the well'bore. The present invention is not primarily concernedwith the character of the cutting means embodied in the bit andcontemplates the employment of cutting means and elements of variousnatures. In the form of the invention being described the cutting meansI2 includes two cuttingblades I1 on the lower end portion of the body I0and a set of spaced cutting blades I8 on the upper enlarged body portionI4. The cutting blades Il may be termed pilot blades and operate to forman annular cut inthe earth formation to receive the lower portion of theshank IU with suitable clearance. The blades Il project downwardly andoutwardly from the lower end of the body I0 and have upwardly andinwardly inclined lower cutting edges and substantially vertical reamingedges. The inner edges of the blades I'I .are clear of or aligned withthe wall of the opening I| to permit the passage of the surveyinginstrument A through the opening. The lower end portion of the body I0may be provided' with stabilizing blades I 9. The blades I9 projectdownwardly and outwardly from the lower end of the body I9 and havequite broad outer surfaces 20 adapted to cooperate with the outer Wallof the cut made by the blades I1 to assist in stabilizing the bit. Itwill be observed that the pilot blades I'I' operate to form an annularcut and leave a central portion or core of earth formation in line withthe opening II. It is preferred to provide notches 2| in the low'er endof the body II) to communicate with the opening I I. The notches 2| areprovided to permit the free lateral discharge of fluid from the openingII and are preferably arranged in front of the blades I1 with respect tothe direction of rotation of the bit.

The upperblades I8 are the reaming or bore enlarging blades of thecutting means I2. The blades I8 project downwardly and outwardly fromthe enlarged tapered /body portion I4. The lower edges 22 of the cuttingblades I8 slope downwardly and outwardly and the outer edges or reamingedges 23 of the blades I8 may be substantially vertical. The blades I8are operable to enlarge the well bore to receive the drilling stringwith substantial clearance to provide for the return oW off circulationfluid through the well bore. I

The means |3 is an important feature of the invention. The means I3 isprovided to remove or cut away the core or inner portion of earthformation during the drilling operations and is retractable to permitthe surveying instrument A to be arranged in or passed through the bodyopening II to make a well survey. The means I3 includes one or moreretractable core breaking or cutting dogs 24. In the particular caseillustrated there is one dog 24, it being understood that the inventioncontemplates the employment of one or more dogs. The core cutting orbreaking dog 24 is preferably located at the lower end portion of thebit body IU and the 'lower part of the body is constructed to receiveand mount the dog. An enlargement or boss 25 is provided on the exteriorof the body I0 in adjoining relation to one of the stabilizing blades I9and a notch 26 extends upwardly into the lower end of the body I0between the boss 25 and the said stabilizing blade I9. The notch 26preferably has fiat parallel side walls and a at substantiallyhorizontal upper wall. The body I0 is provided with a machined or fiatsurface 21 at the outer side of the notch 26 and ya similar flat surface28 on the rear side of the stabilizing blade I9 that is adjacent thenotch 26. The surface 21 is pro-l vided on the outer side of the boss2-5 and the adjacent parts of the body I0.

The core cutting or breaking dog 24' is a shiftable or pivotableknife-like element. The outer portion of the dog 24 is received in thenotch 26.

Means is provided for pivotally supporting the dog 24 in the notch 26. Abore or socket 29 enters the body I0 from the above-mentioned surface28and intersects the notch 26. The inner end of the opening 29 may enterthe boss 25. A pivot pin -30 is arranged in the opening 29 to passthrough a transverse opening 3| in the outer portion of the dog 24. Thepin 30 supports the dog 24 for pivotal movement about a substantiallyhorizontal axis. Welding 308L may be provided on the rear surface 28 ofthe adjacent stabilizing blade I9 to secure the pin 30 in its opening29, it being obvious that other means may be employed to hold the pin 30in place. The opposite sides of the dog 24 are preferably flat to'effectively bear on the side walls of the notch 26 and the upper sideof the dog 24 is iiat to bear upwardly against the upper wall of thenotch 26. When the dog 24 is in its normal substantially horizontalcutting position its upper side is in flush bearing engagement with theflat upper wall of the notch 26.

The dog 24 is proportioned to project into the opening II or to projectinto the central zone directly below the opening II. In practice the dog24 may be proportioned to have its inner end a short distance from thecentral longitudinal axis of the opening II when in the active corebreaking position. The inner projecting portion of the dog 24 may bepointed or. provided with inwardly convergent sides as best illusmatedin rigs. s and 4 of the drawings. A cutv 5 ting rib 32 is provided onthe active lower side ofthe dog 24. The rib 32 may be built up ofwelded-on hard cutting material and is provided to cut away the core ofearth formation left standing between the pilot blades I1. The

' 10 cutting rib 32 operates du'ring rotation of the bit to cut away thecentral core of earth formation by a dragging or shearing action. Theupper .inner corner 33 of the dog 24 is vbevelled or rounded downwardlyand inwardly for the purpose to be hereinafter described. l

The invention may provide means for automatically returning the dog 24to its active cutting position immediately upon the removal of thesurveying instrument A from the opening. II

of the bit. A slot 34 is provided' in the outer portion of the dog 24 tointersect the opening 3|. A torsional spring 35 is arranged in the slot34 and surrounds the pin 36. One end portion of the torsional spring 35bears upwardly against 25 the under side of the dog 24 and the other endportion of the spring bears inwardly against a surface of the body I0.The spring 35 exerts a turning force on the pivoted dog 24 to urge thedog to the active position illustrated in Figs.

1 to 4 of the drawings where its upper side bears against the upper wallof the notch 26..- The engagement of the dog 24 with the earth formationmay automatically return vthe dog to its active position and'it may bepreferred or desirable in some instances to dispense with the springmeans just described.

In the preferred construction the outer side of the dog receiving notch26 is closed to protect the dog' 24 and the other parts against an oexcessive -:flow of iiuid through the notch. A plate 36 is arrangedagainst the body surface 21 and extends across the outer side of thenotch 26. The plate 36 is shaped to conform tov the surface 21 and toextend about the adjacent portion of the dog 24. Welding31 may securethe plate 36 to the body I0. The plate 36 serves to prevent the flow ofcirculation uid laterally through the notch 26 and protects the dog 24.

In the use or operation of the bit the body I0 o is connected with thelower end of the well drilling string and the bit is operated on thelower end of the string in the usual manner. ,During the drillingoperations the drilling string is rotated and the blades I1 and I8 act.on the earth formation to form the well bore.` The blades I1 on thelower end of the bit body I6 form a pilot bore of small diameter inadvanceV of the bore enlarging blades I6. The blades I8 act on the earthformation to enlarge the pilot 0 bore and to make the well bore ofthedesired gauge. The core cutting or breaking dog 24 is in the positionillustrated in Figs. 1 to 4, inclusive, of the drawings, during thedrilling-.operations-and its cutting rib 32 operates to cutaway 5 thecore or central portion of earth formation left standing between theblades I1. It will be observed that the engagement of the cutting dog 24with the earth formation serves to hold the dog in the position whereits upper side bears against the upper wall of the notch 26. Thus theoperating forces are directly transmitted from the body I0 to the dog-24 without subjecting the pivot pin 30 to severe strains. Thecirculation fluid passed downwardly through the drilling string iiowsthrough the opening II and is discharged from its lower end and from thenotches 2|. This circulation fluid may assist in removing the core.'When it is desired to make a survey of the well or to project a wellinstrument into the 5 open well below the bit the drilling operationsare temporarily suspended and the drilling string is moved upwardly toraise the bit from the bottom of the well. The surveying instrument A orother well instrument is then dropped, pumped 10 or run down through thedrilling string to pass through the opening II of the bit body I0. Whenthe instrument A approaches the lower end of the opening II it contactsthe. rounded upper inner corner 33 of'thedog 24 and the down- 15 wardlymoving instrument moves or swings the dog downwardly and outwardly to aposition such as illustrated in Fig. 5 of the drawings. The weight ofthe surveying instrument A is sumcient to overcome'the spring 35 yandreadily move '20 the dog 24 to its`retracted position. Thus theinstrument A is free to pass downwardly through the opening II andproject from the lower end of the bit. The instrument A is adapted tocome to rest in a position where its head, or an en- 25 largement on theinstrument, seats on the flange I6. This locates the instrument and theengagement of the instrument head with the iiange I6 cuts off orsubstantially cuts off the flow of circulation fluid causing the pumpsto stop or 3o labor, thus indicating to the operator or driller that theinstrument is in the correct position for operation. When the instrumentA is in its correct position projecting from the lower end of the bit itis controlled or operated in the usual 36 manner to take a reading.Upon4 the completion of the survey or instrument operation theinstrument A is withdrawn from the drilling string. When the instrumentA is moved upwardly from the opening II the spring 35 swings 40 orpivots the dog 24 upwardly and inwardly to the active position where itsupper side contactsthe upper wall of the notch 26. Thus the corebreaking dog 24 is automatically reconditioned for operation immediatelyupon the removal of 45 the surveying instrument A from the bit. 'I'hedrilling operations may now be resumed.

It is to be observed that the improved bit illustrated in Figsl to 5,inclusive, embodies an improved core breaking means that effectively 50removes the core or central portion of earth formation during drillingand that does not require withdrawal from the well preparatory to makinga well survey or Well condition determining operation. The core breakingdog 24 is car- 55 ried by the bit throughout the drilling and surveyingoperations eliminating the necessity of running a grappling vtool `intoand out of the drilling string before and after the surveying operationto withdraw and reset a core break- 50 ingdevice.

The embodiment of the invention illustratedin Figs. 6, '1 and 8 of thedrawings may be said to comprise, generally, a body 40 having a centralvertical-opening 4I, cutting means 42 on the 65 body 46, and a pluralityof retractable core breaking dogs 43, carried by the body 40 to break orcut away the central portion of the earth formation that would otherwiseenter the opening 4 I.

The bit body 40 may be a generally cylindrical 70 member, asillustrated. Suitable means is provided at the upper end of the body 46foryconnecting itr with the' `drillingstring. In the case illustrated atapered screw threaded socket 44 is provided in the upper end part ofthe body 40 to' 'I6 60 active positions.

receive the pin of the drill collar of the string. The opening 4|extends downwardly from the socket 44 to the lower end of the body 40.

The cutting means 42 may be any suitable form 5' of lmeans for cuttingaway the earth formation and that permits the passage of a surveyinginstrument through the body 40 to project from the lower end of the bit.In the typical case illustrated the cutting means 42 comprises spaceddownwardly and outwardly projecting cutting blades 45 on the lowerportion of the body 40. The blades 45 may be of substantial length tocontinue upwardly along the side of the body 40. The lower cutting edges46 of the blades 45 slope downwardly and outwardly while the sidecutting edges or rearning edges 41 of the blades are substantiallyvertical. The inner edges of the cutting blades 45 are clear of oraligned with the wall of the opening 4| to permit the passage of asurveying instrument downwardly from the the body opening 4|.

The dogs 43 are provided to break away or cut away the central core ofearth formation left by the blades 45 to leave the opening 4| open orunobstructed and to provide a generally flat bottom wall on the well. Inaccordance with the invention there may be any suitable number of corebreaking dogs 43. In the form of the invention being described there aretwo likedogs 43. The dogs 43 are arranged in diametrically oppositeslots or notches 48 in the lower end portion of the bit body 40. Thenotches 48 extend upwardly from the lower end of the bit body andcommunicate with or join the opening 4|. The side walls of the notches48 are preferably flat and 40 parallel and the upper walls 49 of thenotches are flat and generally horizontal. Transverse bores or openings50 are provided in the body 40 to intersect the upper portions of thenotches 48.

In accordance with the invention the dogs 43 are pivotally supported'inthe notches 48 to depend or project downwardly. Pivot pins 5| arearranged in the openings 50 and pass through transverse openings 52 inthe upper parts of the 50 dogs 43 to support the dogs for pivotalmovement having inner faces 53 thatslope downwardly and inwardly whenthe dogs are in their active positions. The lower ends of the dogs 43are provided with hard cutting material 54 and are substantiallyhorizontal when the dogs are in their The upper ends of the dogs 43 areprovided with stop shoulders or faces 55 engageable with the upper walls49 ofthe notches 48 to stop the dogs in their active positions and toassist in transmitting the drilling pressures and forces between thebody l0 and the dogs. The inner lower corners of the dogs 43 arepreferably rounded, as illustrated. The sides of the inner activeportions of the dogs 43 may be inwardly convergent as best illustratedin Fig. 8 of the drawings. The dogs 43 are proportioned to have theirinner lower corners in spaced adjacent relation to the central verticalaxis of the opening 4| when in their active cutting posi- 75 tions.'I'he hard cutting material 54 preferably continues upwardly along therounded inner lower corners of the dogs 43.

Means is provided for yieldingly holding the dogs 43 in their activecutting positions and for returning the dogs to these positionsfollowing the withdrawal of the surveying instrument from the bit. Flatsubstantially vertical surfaces 56 are provided on the periphery of thebody 40 at the outer sides of the notches 48. Leaf springs 51 arearranged against the surfaces 56 and are secured to the body 40 byscrews 58, or the like.

The leaf springs 51 project downwardly into the notches 48 to cooperatewith the pivoted dogs 43. The dog controlling springs 51 are shaped tobear inwardly against the outer sides of the dogs 43 to urge the dogs totheir active positions where the stop faces 55 cooperate with the upperwalls 49 of the notches 48. Plates 60 are welded to the body surfaces 56to extend across the outer sides of the notches 48. The plates 80 extenddownwardly from the upper ends of the notches 48 to adjacent the lowerend of the body 40 and serve to protect the dogs 43 and the springs 51.The plates 60 prevent an excessive flow of circulation fluid through thenotches 48 thus protecting the dogs 43 and the springs 51 against theerrosive action of the uid.

In the use or operation of the bit illustrated in Figs. 6, 7 and 8 thebody 40 is connected with the lower end of the drilling string and thestring is rotated and fed downwardly in the well in the usual manner.The cutting blades 45 serve to cut the well bore to gauge but leave acentral portion or core of earthformation. The dogs 43 are in thepositionsv shown in full lines in the drawings during the drillingoperation and serve to cut away the core of earth formation justmentioned. It is to be observed that the dogs 43 are formed and mountedso that the cutting pressures are transmitted longitudinally throughthem and through the cooperating stop faces 55 and the upper ends of thenotches 48. The cut- 'ing engagement of the dogs 43 with the core ofearth formation maintains -the dogs in their active cutting positions.The hard cutting material 54 makes thedogs 43 particularly effective indrilling or breaking away the core. Circulation fluid pumped downwardlythrough the drilling string discharges from the lower end of the opening4| to flush the dogs 43 and the cutting blades 45.

When it is desired to make a survey of the well, or a so-called "openhole reading, the bit is raised from the bottom of the well and thesurveying instrument is dropped or lowered through the drilling string.When the surveying instrument moves downwardly through the body opening4| its lower end contacts the inner sides 53 of the dogs 43. Thesurveying instrument engaging the inclined sides 53 readily swings thedogs 43 outwardly to the retracted positions illustrated by the brokenlines in Fig. '1. 'Ihus the downwardly moving surveying instrumentautomatically retracts the dogs 43. The instrument is free to projectfrom the lower end of the bit and when in the correct position isoperated to make the survey. Upon the completion of the survey theinstrument is withdrawn upwardly from the bit and removed from thedrilling string. Upon the upward withdrawal of the surveying instrumentfrom the opening 4| the springs 51 acting on the dogs 43 automati-`cally pivot the dogs to their active cutting positions. The bit may thenbe lowered to engage or outer sides of the elements 14.

the bottoml of the well borefand the drilling operation may becontinued.

Fig. 9 of the drawings illustrates a portion of a well bit embodyinganother form of the invention. VIn the structure shown in Fig'. 9,10designates a well bitbody having a central vertical opening 1l adaptedto receive a surveying instrument, or the like. Suitable cutting meansis provided on thebit body 10 to `cut the major outer portion of thewell. In the'case illustrated this cutting :means comprises suitable.drag type blades 12 projecting downwardly and outwardly from the body10. 'The blades 12 are arranged so that an object such as a surveyinginstrument may be passed downwardly through the opening 1| to projectfrom the lower end of the bit. In this form of the invention there areone or more lateral pockets 13 provided in the body 18 to communicatewith its opening 1I. In the case illustrated thereare two diametrlcallyopposite pocketsv 13 formed in the body 10.

A core breaking or core cutting element 14 is bodily shi'ftable in eachpocket 13 between a position Where it projects into the opening 1I tocut away the core or inner portion of thev earth formation and aposition retracted within the pocket. The elements 14 are knife-like orbladelike parts having lower cutting edges 15 that may be hard faced orprovided with hard cutting material. The upper inner corners of theelements 14 are bevelled oi to provide downwardly and inwardly inclinededges 18. The upper ends of the elements 14 may be flat to bear againstthe upper walls of the pockets 13 when the elements are in. theirprojected active positions.

Means are provided for governing the movement of the core breaking andcutting` elements 14. In the case illustrated these means comprisedownwardly and outwardly inclined slots 11 in the elements 14 and pins18 carried by the body 10 to intersect the pockets 13 and pass throughthe slots 11. The engagement of the pins 18 with the slots 11 may besuch that it prevents undesirable pivoting or rocking of the elements 14on the pins. 'Ihe elements 14 are movable downwardly and outwardly onthe pins 18 from the active positions illustrated to retracted positionsentirely within their pockets 13. Spring means may be provided to returnor to assist in returning the elements 14 to their active projectingpositions. We have shown leaf springs 19 secured to the body 10 andprojecting into the pockets 13 to bearinwardly against the rear Thesprings 19 are positioned and shaped to urge the elements 14 upwardlyand inwardly.

The operation of the bit construction illustrated in Fig. 9 of thedrawingsis substantially identical with the previously described forms.of the invention. During drilling operations the elements 14 are in thepositions illustrated so that their lower cutting edges 15 act on theinner or central portion of the earth formation to cut the same away.The blades 12 form the outer portion of the well. When a survey orsimilar operationis to be performed the bit is raised and the surveyinginstrument or like device is'run down through the opening 1I to projectbeyond the lower end of the bit. The lower end of the surveyinginstrument contacts the edges 18 and forces or moves the elements 14downwardly and outwardly. Thus the surveying instrument automaticallyretracts the elements 14. When the surveying instrument is Withdraw Immthe bit 'the springs 19 urge the elements14 upwardly and inwardly toprotrude into the opening 1l and when drilling operations are resumedthe engagement of the earth formation with thecutting edges 15positively returns the elements 14 to their fully extended activepositions.

Having described only typical preferred forms and applications of ourinvention, we do not wish to be limited or restricted to the specificdetails herein set forth, but wish to reserve to ourselves anyvariations or modillcations that may appear to those skilled in the `artor `fall within the scope of the following claims:

Having described our invention, we claim:

1. A well drilling bit comprising a body having a vertical opening,cutting means on the 'body operablel to Imake an annular cut in theearth formation leaving a central core of earth formation, an elementpivotally supported on the body, and yielding means urging the elementto a posi-l tion where it cuts away the core. and where it isretractable by an object run down in the opening to allow the projectionof the object from the lower end of the body and operable to return theelement to the core cutting position.

2. A rotary well drilling bit comprisingl a body having an openingadapted to pass an object to be run into the well, cutting means on thebody arranged to allow the passage of said instrument from the lower endof the opening, a corebreaking dog pivoted on `the body to swing about agenerally horizontal axis, means limiting upward -pivoting of the dog tostop the dog in a position and spring means yieldingly urging the dog tothe cutting position.

3. A rotary well drilling bit comprising a body having an openingadapted to pass an object to be run into the well, cutting means on thebody arranged to allow the passage of said instrument from the lower endof the opening, a core breaking dog pivoted on the body to swing about agenerally horizontal axis, means limiting upward pivoting of the dog tostop the dogin a position where it cuts away the central portion ofearth formation during drilling and is engageable by an object passeddown through the opening to be retractable downwardly and outwardlythereby, and a spring reacting against the body and dog for returningthe dog to the cutting position upon upward withdrawal of the objectfrom the opening.

4. A rotary well'drilling bit ycomprising a body having an openingadapted to pass an object, cutting means on the ybody arranged to allowthe passage of said object from the lower end of the opening, aplurality oi core breaking dogs piv- 'otally supported on the body toremove' the cenbody to be secured to a' drilling string and having avertical opening for *receiving an object to be run into the well andhaving a lateral notch joining said opening, cutting means on the bodyclear of said opening to pass said object from the lower end of thebody, and a core breaking dog pivoted in said notch to normally projectinwardly and cut away the core left by the cutting means and pivotabledownwardly and outwardly portion of earth formation left by said cuttingmeans and yieldable to allow downward and outward retraction of thevelement from the openingv by the said object, and stop means limitingupward `and inward pivoting of the element to stop the element in aposition to cut away said portion of the earth formation. A

7. A rotary well drilling bit comprising a bit body to be secured to adrilling string and having a vertical opening for receiving an objectrun through the string and having a lateral notch joining said opening,cutting means on the body yclear of said opening to pass said objectfrom the lower end of the body, a core breaking element, means pivotallysupporting the element in the notch for movement between a positionwhere it bears against the upper wall of the notch and projects towardthe central vertical axis of the bit to cut away -the central portion ofearth formation and a position where it projects downwardly clear of thesaid opening, and spring means urging the element to the iirst mentionedposition and yieldable to allow movement of the element to the secondmentioned position when the object moves down against the element.

8. A rotary well drilling bit comprising a body having a verticalopening for receiving an object to be run into the well and having anotch communicating with said opening, cutting means on the body clearof said lopening to pass said object from the lower end ofthe body, acore breaking element, means pivotally supporting the element in thenotch for movement between a position where it bears against the upperwall of the notch and projects toward the central vertical axis of thebit to cut away the central portion of earth formation and a positionwhere it projects downwardly clear of the said opening, and meansurglngthe element to the rst mentioned position and yieldable to allowmovement of the element to the second mentioned position when the objectmoves down against the element,

the last named means including a torsional spring acting on the element.

9. A rotary well drilling bit comprising a body having a verticalopening for receiving an object to be run into the well and having anotch communicating with said opening, cutting means on the body clearof said opening to pass said object from the lower end of the body, acore breaking element, means pivotally supporting the element ln-thenotch for movement between a position where it bears against the upperwall-of the notch and projects toward the central vertical axis of thebit to cut away the central portion of earth formation and a positionwhere it projects downwardly clear of the said opening, and means urgingthe element to the rst mentioned position and yieldable to allowmovement of the element to the second mentioned position when the objectmoves down against the element, the last named means including a leafspring acting on the element.

THOMAS E. McMAHAN.

THOMAS A. CREIGHTON.

